Date: September 18, 2018
Source: Cell Press
Noticing that songbirds, such as
finches, never seem to get fat despite overeating at bird feeders, London
environmental biologist Lewis Halsey wondered whether the amount of energy
birds put into singing, fidgeting, or exercising could be adjusted in ways that
regulate weight. In a literature review published September 18 in the
journal Trends in Ecology & Evolution, he explores whether songbirds
don't need to worry about their calorie counts because they can control the way
their bodies use energy.
"The passerine birds at the
bird feeders near my home never seem to get fat despite having this buffet
constantly available to them, but there are people who get heavy when exposed
to that kind of all-you-can-eat environment," says Halsey of the
University of Roehampton. "I wanted to investigate possible behavioral and
physiological mechanisms, aside from just food consumed and exercise completed,
that help animals control their energy budgets and body weights; there's more
going on than just how many calories you've put into your face."
Now, it could be that we never
see fat songbirds because the ones that gain too much weight are picked off by
a range of predators. However, that predation pressure would eventually cause
evolution to weed out such a tendency, and recent studies indirectly suggest
that birds are capable of balancing energy intake by increasing their daily
metabolic rate or decreasing the efficiency with which they are able to extract
energy from ingested food.
"For a given amount of food,
an animal can unconsciously adjust how efficiently it uses the energy from it
either behaviorally, for example by changing wingbeat frequency or singing
patterns to use more or less energy, or physiologically, in terms of digestive
or cellular metabolic efficiency," Halsey says.
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